How to make a bone NOT inherit location from parent? Or how to position bone at world location?
This can be done with bone constraints


Add an Empty to the Scene at the base of your child bone. 
Disconnect the child bone from its parent (AltP) in Armature Edit Mode. 
In Pose Mode select the child bone, go to the Bone Constraints context , and add a Copy Location Constraint targeted at the Empty.


Here is an example of the result:



Above: An armature object being moved while one of its bones remains stationary